1. Field of the Invention
The present invention relates to a magnetic resonance imaging apparatus in which a high frequency receiving coil includes a plurality of coil elements or the high frequency receiving coil can be mounted with the plurality of coil elements, a signal selection method in the magnetic resonance imaging apparatus, and a magnetic resonance imaging method in the magnetic resonance imaging apparatus.
2. Description of the Related Art
In recent years, a magnetic resonance imaging apparatus can utilize various types of high frequency receiving coils according to the purpose. In some of the high frequency receiving coils, a plurality of coil elements is arranged. In addition, some of the high frequency receiving coils is also provided with, for example, local coils corresponding to different picture portions.
As such, the magnetic resonance imaging apparatus is configured such that a plurality of coil elements arranged in a high frequency receiving coil or a plurality of kinds of high frequency receiving coils is connected in parallel, and the number of coil elements or high frequency receiving coils is increasing. For example, there is a magnetic resonance imaging apparatus in which 128 coil elements can be connected in parallel.
In such magnetic resonance imaging apparatus, a technique of transmitting output signals of a plurality of coil elements in a frequency-multiplexing manner is disclosed in JP-A-2002-143122, for example.
On the other hand, all of the coil elements connected in parallel are not used at the same time. Therefore, the number of processing systems for processing the output signals from the coil elements is set to be less than the number of coil elements which can be connected to one another. For example, 32 processing systems are prepared for the 128 coil elements.
In this case, since an output signal from a coil element to be used needs to be selectively input to a corresponding processing system but the number of combinations of the coil elements and the processing systems is large, a selection circuit becomes very complicated. A matrix switch is generally used for the selection circuit. The matrix switch needs to have a matrix of s×s in order to freely select some of the ‘s’ coil elements. When the selection circuit is formed by connecting a plurality of matrix switches to one another, each having a matrix of q×q (q<<s), in a multiple stage, the size of the selection circuit becomes smaller than that of a matrix switch having a matrix of s×s. However, in this case described above, the number of combinations of selectable coil elements is limited. This causes a problem in convenience.